1. Field of the Invention
The present invention relates to a centrifuge rotor and tube holder design, and more particularly, to a rotor assembly for producing a relatively low power, low audible level, cool running centrifuge.
2. Background Art
Centrifuges are commonly used in medical and biological research for separating and purifying materials of differing densities such as viruses, bacteria, cells, proteins, and other compositions. A centrifuge normally includes a motor, a rotor, and specimen holders capable of spinning up to tens of thousands of revolutions per minute. Specimen holders include, for example, test tubes, test tube holders, or any other means that is suitable for retaining a specimen.
A preparative centrifuge rotor has some means for accepting specimen holders or “buckets” containing the samples to be centrifuged. Preparative rotors are commonly classified according to the orientation of the sample tubes or buckets. Vertical tube rotors carry the sample tubes or buckets in a vertical orientation, parallel to the vertical rotor axis. Fixed-angle rotors carry the sample tubes or buckets at an angle inclined with respect to the rotor axis, with the bottoms of the sample tubes being inclined away from the rotor axis so that centrifugal force during centrifugation forces the sample toward the bottom of the sample tube or buckets. Swinging bucket rotors have pivoting tube carriers that are not horizontal when the rotor is stopped and that pivot the bottoms of the tubes outward under centrifugal force.
With current swinging bucket rotor designs, the centrifuge buckets are primarily left uncovered by the rotor and generate considerable aerodynamic drag. This drag increases as the non-aerodynamic features move further away from the axis of rotation. Although these aerodynamic features significantly impact upon rotor operations at speeds lower than 3,000 RPM, they can be an even more significant factor at higher RPMs. Because many newer laboratory and forensic protocols require much higher rotational speed during centrifugation, including up to, and well exceeding, 4,000 RPM, identifying efficient and cost effective means of reducing aerodynamic drag is desirable. With current rotor technology, the curved shape of the centrifuge buckets prevents the buckets from retracting into the rotor housing to completely seal the voids therein. Thus, significant aerodynamic drag is generated during centrifugation due to air entering the rotor through these voids.
Centrifugation generally involves rotating a sample solution at high speed about an axis to create a high centrifugal force to separate the sample into its components based upon their relative specific gravity. The sample is carried in a rotor which is placed in a centrifuge chamber in a centrifuge instrument. The rotor is driven to rotate at high speed by a motor beneath the centrifuge chamber. At high speed operations, aerodynamic drag on the rotor becomes increasingly significant. Significantly more power is required to overcome the aerodynamic drag at high speed. In addition, cooling means must be provided to offset the heat generated by aerodynamic friction. Some centrifuges are provided with means for drawing a vacuum or partial vacuum in the centrifuge chamber in an effort to reduce the aerodynamic drag; however, cooling can still be necessary.
In the past, cooling of the centrifuge chamber has been accomplished by attaching refrigerant coils to the outside of the centrifuge chamber (see, e.g., U.S. Pat. No. 5,477,704 to Wright). In such a configuration, a space must be provided between adjacent passages to allow for welding (e.g. at 19 and 20), which reduces the available surface area for efficient heat transfer from the chamber. Significant drawbacks of this design are that cooling or refrigerating the chamber is expensive and prone to malfunction. Accordingly, there is a need for a simple, cost effective means of reducing aerodynamic drag and resulting friction heat with certain swinging bucket rotor designs.